| Human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) invade the central nervous system (CNS) early in infection. However, HIV-associated neurological disorders do not take place until late in the disease process. Thus, elucidating the molecular mechanisms of HIV/SIV gene expression in the CNS is imperative for understanding neuropathogenesis. CCAAT/enhancer binding protein (C/EBP)beta and C/EBP sites in the HIV-LTR are crucial for HIV transcription and replication in monocyte/macrophages, the major productively infected cells in the CNS. In these cells, interferon (IFN)beta-mediated downregulation of HIV/SIV LTR activity and viral suppression involves induction of liver-enriched transcriptional inhibitor (LIP), the dominant-negative isoform of C/EBPbeta. However, the functional roles of the SIV-LTR C/EBP sites remain unknown. Furthermore, no study has investigated sequence variation within these sites throughout disease progression in the brain and periphery.;In this dissertation, we defined the roles of JC1 and DS1 C/EBP sites located within the SIV-LTR core promoter. We also examined the binding properties of C/EBPbeta and LIP to these sites. We found that the JC1 C/EBP site is important for basal-level transcription, while the DS1 C/EBP site is crucial for viral replication in primary macrophages. Additionally, either site is sufficient for mediating IFNbeta-induced suppression of LTR activity.;Using a SIV macaque model, we investigated sequence variation within the SIV-LTR in brain and spleen of macaques euthanized at 10, 21, 42, and 84 days postinoculation (p.i.). We identified a viral variant with nucleotide substitutions within the DS1C/EBP site (DS1C/A) that was absent between 10-21 days p.i. in the brain, but detected at a higher frequency than wild-type genotype from 42- 84 days p.i. in the brain and spleen. Functional analysis of the DS1C/A genotype indicated that although susceptible to IFNbeta treatment, it had increased infectivity and a higher affinity for C/EBPbeta and LIP compared to wild-type genotype. In conjunction with our previous studies we propose a mechanism for the roles of the JC1 and DS1 C/EBP sites in establishing SIV latency in macrophages within the brain, early, followed by the selective replication of virus with the variant DS1C/A genotype during late stages of disease. |
